Intravascular stents are primarily used to open and scaffold tubular passages or lumens such as blood vessels, biliary ducts and the esophagus. They usually consist of expandable lattice meshes that can deploy and hold endovascular grafts, arterial endoprosthesis and self-expanding heart valve implants.
An increasing demand for endovascular stents has lead to significant advancements in the field of analysis, modeling and design. Despite intense research on the subject, some challenges have not yet been fully addressed. For example, over a ten year period of expected lifespan, a stent may undergo nearly four hundred million load cycles, arising mainly from pulsating blood pressure and body movement. Such a cyclic loading drastically amplifies the effect of stress concentration, which may severely reduce the fatigue life of the stent and may eventually lead to fatigue failure.
Peak stresses due to stress concentrations tend to occur in the lattice structures of known prior art stents, which lead to fatigue life issues and other undesirable characteristics. More particularly, lattices formed of closed cells having uneven shapes or curved boundaries having abrupt changes in geometry will tend to cause undesirable stress concentrations. Peak stresses due to stress concentration are also a crucial factor in the delamination of a polymer coating from an arched region of a lattice stent. This phenomenon has the potential to contribute to thrombus formation and can lead to in-stent restenosis and/or change of drug release rate for drug eluted stents.
Therefore, there is a need for an improved stent design.